AST 324: HOMEWORK 1

What is the highest frequency electromagnetic wave that would
be considered an infrared wave? How much energy would be carried
by one photon of this wave? Answer the same question for visible
light, ultraviolet light, X-rays, and radiowaves.

Would we want to make the reflecting surface of a telescope
out of a blackbody? Why or why not? How warm would a blackbody
have to be in order for lambdamax
to be at the longest lambda of infrared
light? Answer also for visible, ultraviolet, X-rays and
gamma-rays.

A spectral line of hydrogen is observed from a distant galaxy
at a wavelength of 657.36 nm (1 nm = 10-9
meters). If this same spectral line is emitted by gas in our own
galaxy, we observe it at a wavelength of 656.70 nm. What can you
conclude from these facts?

A galaxy recedes from us at 60% of the speed of light. By
what factor must we multiply the wavelength of the photon emitted
by the galaxy to get the wavelength as observed by us? What is
the redshift z of this galaxy?